Annealing UHMWPE (ultra-high molecular weight polyethylene) sheets before or after processing helps release internal stress, prevent warping, and improve dimensional stability, especially after CNC processing or compression molding.
Purpose of annealing of UHMWPE sheet
Reduce stress inside the sheet (avoid deformation)
Improve dimensional stability (higher precision after processing)
Reduce crystal defects and improve mechanical properties
Improve subsequent processing performance (such as turning, milling, etc.)
Steps of annealing of UHMWPE sheet
1. Sheet preparation
Clean the surface of the sheet
Ensure that the sheet is free of impurities and oil
The sheet should be laid flat naturally to prevent bending due to force
2. Heating stage
Place the sheet in a hot air circulation furnace or a constant temperature oven
Slowly heat up to 120~130°C
Control the heating rate at 10–20°C/hour
Avoid rapid heating to prevent thermal shock and warping
3. Insulation stage
Insulate at the target temperature (120–130°C) for 2–6 hours
It is recommended that thick sheets be kept warm for a longer time (refer to at least 1 hour for every 10mm thickness)
The temperature needs to be stable and evenly distributed
4. Cooling stage
Turn off the heating and slowly cool down to room temperature
The cooling rate is recommended to be < 10°C/hour
Can be cooled naturally or programmed, the board still needs to be kept horizontal
Notes
During the annealing process, the board must not be compressed or bent, otherwise, it will form permanent deformation
After multiple processing/cutting processes, annealing can be repeated for better results
It is not recommended to use fast heating methods such as open flames and drying lamps, which can easily cause decomposition or warping.
